The present invention relates to a method and apparatus for making lined concrete pipe sections. The invention relates specifically to a way of ensuring that a proper bond is formed between the concrete and the liner of lined concrete pipe section.
Vinyl liners have been used in the manufacture of concrete pipe sections for many years. The vinyl materials used for this purpose is usually composed of high molecular weight vinyl chloride resin with chemical resistant pigments and plasticizers. The material is extruded in sheets. Ribs project from one side and the opposite side is smooth. The ribs are T-shaped and are designed to be embedded in and positively engage the inside wall of a concrete pipe section. The extruded vinyl sheet has a low co-efficient of friction. Therefore, even though the ribs are shaped to engage and retain the liner in close contact with the concrete, it is generally difficult to obtain a good bond because of the nature and texture of the extruded vinyl.
A good bond between the vinyl and the concrete is important to prevent inward collapse of the liner which could result in pipe blockage. Also, a good bond will protect the interface between the vinyl and the concrete from deterioration. In addition, a good bond will resist groundwater pressure created by water on the back of the liner.
One way to achieve a proper bond is to wet cast concrete around a well supported liner and wait a substantial length of time before removing the liner supports. Such wet cast methods are effective but slow and, therefore, expensive.
Attempts have been made to apply dry cast pipe forming techniques to make lined pipes. The short turnover of forming equipment used in dry cast methods is desirable because such equipment can be costly to purchase or rent. However, the texture and bonding characteristics of dry cast concrete mixtures make it difficult to obtain a good bond in short periods of time.
A known dry cast technique uses a non-expandable core around which the liner is loosely fitted. Retaining rings are used to hold the liner in contact with the core as the dry cast concrete is placed into a form and around the liner. However, in order to completely fill the form, the retaining ring must be removed, leaving the liner unsupported. As the core is lifted away from the liner, radial supports are installed to hold the liner in contact with the hardening concrete. However, the radial supports do not fully support the liner and prior to their installation, the liner is substantially unsupported.
In another known system, an expandable core is permanently located at and is part of a stationary form. The liner is initially attached to a carrying cartridge which allows the liner to be placed onto the expandable core at the forming station. The core is expanded hydraulically to support the liner. Dry mix concrete is then placed around the liner/core assembly, while the core is radially expanded. However, since the expandable core is permanently located at the forming station, it is impractical to wait a sufficient period of time to ensure a proper bond at the concrete/liner interface. Another problem with this system is the difficulty of making sure that the radially expanding core is properly shaped to meet pipe design specifications for roundness. The spiral nature of its expansion makes ensuring roundness difficult.
Both of the above described methods for making vinyl lined concrete pipe using the dry cast method have significant problems relating to both cost and quality.
It is therefore an object of the present invention to provide a method for making lined pipe of high quality at low cost.
Another object of the present invention is to provide a method of using dry cast concrete techniques to form lined pipe rapidly without sacrificing quality.
Still another object of the present invention is to provide a method of using dry cast forming techniques to make lined concrete pipe which has proper roundness.
Yet another object of the present invention is to provide a method of forming lined concrete pipe in which the lining is thoroughly bonded to the concrete.
A further object of the present invention is to provide an apparatus which can be used to quickly make lined concrete pipe which has excellent roundness and which has an excellent bond between the lining and the concrete.
These and other objects are achieved with a method of making lined concrete pipe sections in which a liner is placed around an expandable and moveable core. The core is placed over a module which causes the core to deflect to a round cylindrical shape. Reinforcing material and an outer form are placed over the liner/core/module assembly, and the form is filled with dry mix concrete. After vibrating the concrete into its final position, the form/liner/core assembly is lifted from the module. The core can remain in full contact with the liner to prevent any delamination of the liner from the concrete during stripping of the outer form and during subsequent curing of the concrete. Importantly, the stripping and curing with the core in place can occur at a location remote from the module. The module, therefore, and the form filling and vibrating equipment can be used frequently without any sacrifice in liner-to-concrete bond quality. In addition, pipes made in such a manner will have the excellent quality provided by centering and shaping functions of the module.